For what it's worth, I spent best part of a year using various screens and finally settled on a GrandView.
Amazingly bright picture and a very unique mounting solution.
They may not be so very well known in the UK yet, but in Europe it's the Rolls Royce of screens.
Beautifuly engineered piece of kit.
At the risk of sounding obvious, choosing a good quality screen is paramount in obtaining a clean, bright picture and prepare to spend hours adjusting the projector settings to get the correct white balance.
Plasma and LCD big screens are great, but nothing beats a good projection system for the ultimate cinema experience.
Try watching the 3D BluRay of Coraline on a well calibrated screen and after a few minutes you are literally drawn into the movie.
Talking of which, my ultimate experience has to be The Dark Knight in the Printworks IMAX in Manchester, that was trippy!